object-name.h: move declarations for object-name.c functions from cache.h

Signed-off-by: Elijah Newren <newren@gmail.com>
Acked-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/range-diff.c b/range-diff.c
index d1ed3b8..a299433 100644
--- a/range-diff.c
+++ b/range-diff.c
@@ -2,6 +2,7 @@
 #include "environment.h"
 #include "gettext.h"
 #include "range-diff.h"
+#include "object-name.h"
 #include "string-list.h"
 #include "run-command.h"
 #include "strvec.h"